The Borrowing Hydrogen Strategy by Supported Ruthenium Hydroxide Catalysts: Synthetic Scope of Symmetrically and Unsymmetrically Substituted Amines

The N-alkylation of ammonia (or its surrogates, such as urea, NH4HCO3, and (NH4)(2)CO3) and amines with alcohols, including primary and secondary alcohols, was efficiently promoted under anaerobic conditions by the easily prepared and inexpensive supported ruthenium hydroxide catalyst Ru(OH)(x)/TiO2. Various types of symmetrically and unsymmetrically substituted tertiary amines could be synthesized by the N-alkylation of ammonia (or its surrogates) and amines with primary alcohols. On the other hand, the N-alkylation of ammonia surrogates (i.e., urea and NH4HCO3) with secondary alcohols selectively produced the corresponding symmetrically substituted secondary amines, even in the presence of excess amounts of alcohols, which is likely due to the steric hindrance of the secondary alcohols and/or secondary amines produced. Under aerobic conditions, nitrites could be synthesized directly from alcohols and ammonia surrogates. The observed catalysis for the present N-alkylation reactions was intrinsically heterogeneous, and the retrieved catalyst could be reused without any significant loss of catalytic performance. The present catalytic transformation would proceed through consecutive N-alkylation reactions, in which alcohols act as alkylating reagents. On the basis of deuterium-labeling experiments, the formation of the ruthenium dihydride species is suggested during the N-alkylation reactions.